1. Field of the Invention
The present invention relates to a display device and a method for producing the same. In particular, the present invention relates to a display device which reliably emits light at a desired luminance, and a method for producing the same.
2. Background of the Invention
FIG. 38 shows an example of a large screen display in which a plurality of display devices are arranged on an optical waveguide plate. The large screen display 100 has, for example, such features that it is of the direct vision type, it is of the thin type, it has a high luminance, and it has a wide angle of visibility. A plurality of display devices 10 as described later on are arranged in the vertical direction and in the lateral direction respectively on a first surface (back surface) of the large optical waveguide plate 102 which is composed of, for example, glass or acrylic to construct the large screen display of the thin type. In addition to the ordinary display having an oblong configuration, it is possible to form screens having a variety of shapes including, for example, those having a rectangular configuration with a longer horizontal length, those having a rectangular configuration with a longer vertical length, and those having a circular configuration, by arbitrarily changing the arrangement of the display devices 10. It is also possible to form a curved surface display by previously curving the optical waveguide plate.
FIG. 39 shows a schematic cross section of the display device 10. The display device 10 comprises an actuator substrate 12, an optical waveguide plate 14, and a plurality of crosspieces 16 allowed to intervene between the both. The optical waveguide plate 14 and the crosspieces 16 are joined to one another by the aid of an adhesive 17. The actuator substrate 12 has an actuator element 18 which is displaceable toward the actuator substrate 12 or toward the optical waveguide plate 14 at a position surrounded by the plurality of crosspieces 16. A unit dot 22 is constructed by the actuator element 18 and a picture element assembly 20 which is provided on the actuator element 18. As described later on, the display device 10 is provided with a plurality of unit dots 22.
The unit dot 22 is specifically constructed as follows. That is, a hollow space 24 is formed at the inside of the actuator substrate 12 corresponding to the position at which the actuator element 18 is provided. Therefore, the portion of the actuator substrate 12, at which the actuator element 18 is provided, has a thin wall thickness as compared with the other portions (the portion will be hereinafter referred to as “thin-walled sections” 12a).
The actuator element 18 comprises a shape-retaining layer 26 which is composed of a piezoelectric/electrostrictive material or an anti-ferroelectric material, a column electrode 28 which is provided on the lower surface of the shape-retaining layer 26, and a row electrode 30 which is formed over a range from the side surface to the upper surface of the shape-retaining layer 26 with a through-hole 13 provided through the actuator substrate 12 from the lower surface of the actuator substrate 12.
The picture element assembly 20, which is formed on the actuator element 18, is a laminate comprising a light scattering element layer 32, a color filter layer 34, and a transparent layer 36. As described later on, when the picture element assembly 20 abuts against the optical waveguide plate 14, the light 38, which is guided through the inside of the optical waveguide plate 14, is reflected. In this process, the light 38 is colored to have a color corresponding to a color of the color filter layer 34, and the light 38 is emitted to the outside of the optical waveguide plate 14. Accordingly, the unit dot 22 emits light with the color corresponding to the color filter layer 34.
Therefore, when the color of the color filter layer 34 is varied for each of the unit dots 22 so that the light emission is obtained with the red color for a certain unit dot 22, the green color for another unit dot 22, and the blue color for still another unit dot 22, then the entire display device 10 is provided with the three primary colors of light. Therefore, the display device 10 is capable of emitting all colors. In the following description, a group, in which one or more unit dots 22 for causing red light emission, is referred to as “red dot”, and it is designated by reference numeral 22R. Similarly, groups, in which one or more unit dots for causing green light emission and blue light emission, are referred to as “green dot” (designated by reference numeral 22G) and “blue dot” (designated by reference numeral 22B) respectively.
In general, as shown in FIG. 40, the red dot 22R, the green dot 22G, and the blue dot 22B are arranged in an aligned manner. A picture element (pixel) 40 is constructed by them. The display device 10 comprises a plurality of such picture elements 40, and it displays a variety of colors depending on the light emission states of the red dot 22R, the green dot 22G, and the blue dot 22B. As a result, an image is displayed on the large optical waveguide plate 102 of the large screen display 100.
In the display device 10 constructed as described above, as shown in FIG. 39, when the upper end surface of the picture clement assembly 20 (transparent layer 36) abuts against the optical waveguide plate 14, then the light 38, which is guided through the inside of the optical waveguide plate 14, is transmitted through the transparent layer 36 and the color filter layer 34, and then it is reflected by the light scattering element layer 32. The light is emitted as scattered light 42 to the outside of the optical waveguide plate 14. As a result, the display device 10 causes light emission with the color corresponding to the color filter layer 34.
When the voltage is applied between the column electrode 28 and the row electrode 30, for example, if the column electrode 28 is the positive electrode, then the electric field, which is directed from the column electrode 28 to the row electrode 30, is generated. As a result, the polarization is induced in the shape-retaining layer 26, and the strain, which is directed to the column electrode 28, is generated in the shape-retaining layer 26. As shown in FIG. 41, the strain causes bending deformation of the actuator element 18. The entire actuator element 18 is displaced downwardly, and the upper end surface of the picture element assembly 20 is separated from the optical waveguide plate 14. In this situation, the light 38 is not reflected by the picture element assembly 20, and it is guided through the inside of the optical waveguide plate 14. Therefore, the light 38 is not emitted to the outside of the optical waveguide plate 14. That is, in this situation, the display device 10 is in the light off state.
When the applied voltage is changed so that the difference in electric potential between the both electrodes 28, 30 is decreased, the strain of the shape-retaining layer 2526 is removed in accordance with a hysteresis manner. That is, the strain of the shape-retaining layer 26 is scarcely removed at the beginning at which the difference in electric potential between the column electrode 28 and the row electrode 30 is initially decreased. When the difference in electric potential is further decreased, the strain is quickly removed. Finally, the upper end surface of the picture element assembly 20 abuts against the optical waveguide plate 14 again, and thus the display device 10 is in the light emission state (see FIG. 39).
As clearly understood from the above, the luminance and the light emission color of the display device 10 can be adjusted by adjusting the difference in electric potential between the column electrode 28 and the row electrode 30. Further, it is possible to switch the display device 10 from the light emission state to the light off state, or from the light off state to the light emission state.
The light emission state or the light off state of the display device 10 is entirely displayed on another surface (principal surface) different from the surface of the large optical waveguide plate 102 on which the display devices 10 are arranged. That is, the principal surface functions as the display screen of the large screen display 100.
The display device 10 is produced, for example, as follows. At first, a plurality of segment plates composed of fully stabilized zirconium oxide or the like are placed on a flat plate composed of fully stabilized zirconium oxide or the like. Further, a thin-walled flat plate composed of fully stabilized zirconium oxide or the like is placed on the segment plates.
The sintering treatment is applied in this state to join these components to one another. Thus, the actuator substrate 12, which has the hollow space 24 and the thin-walled section 12a, is obtained. The through-hole 12b, which extends from the lower surface of the actuator substrate 12 to the hollow space 24, is previously provided before the sintering treatment. Accordingly, it is possible to suppress any deformation of the substrate 12 which would be otherwise caused by the sintering treatment, because of the following reason. That is, even when the gas in the gap to be formed into the hollow space 24 is expanded during the application of the sintering treatment, the amount of the gas corresponding to the expansion is discharged to the outside through the through-hole 12b. 
The through-hole 13 is formed by mutually superimposing through-holes which are previously provided through the flat plate, the segment plate, and the thin-walled flat plate respectively, or by providing the through-hole through the substrate 12 after the sintering treatment.
Subsequently, the column electrode 28, the shape-retaining layer 26, and the row electrode 30 are formed in this order by means of the film formation method including, for example, the photolithography method, the screen printing method, the dipping method, the application method, the electrophoresis method, the ion beam method, the sputtering method, the vacuum vapor deposition method, the ion plating method, the chemical vapor deposition (CVD) method, and the plating. Thus, the actuator element 18 is provided on the actuator substrate 12.
Subsequently, a precursor of the crosspiece 16 is formed so that the actuator element 18 is surrounded thereby. That is, a thermosetting resin is deposited on the actuator substrate 12 so that the actuator element 18 is surrounded thereby. The adhesive 17 is applied to the upper end surface of the precursor of the crosspiece 16.
Subsequently, a precursor of the light scattering element layer 32, a precursor of the color filter layer 34, and a precursor of the transparent layer 36 are formed in this order on the actuator element 18. Accordingly, a precursor of the picture element assembly 20 is obtained. The respective precursors can be also formed by means of the film formation method as described above.
Subsequently, the optical waveguide plate 14 is placed on the upper end surface of the precursor of the crosspiece 16 and the precursor of the picture element assembly 20. The pressure is applied from both of the upper surface of the optical waveguide plate 14 and the lower surface of the substrate 12.
The entire body is subjected to the heat treatment in this state to simultaneously harden the precursor of the crosspiece 16, the adhesive 17, and the picture element assembly 20. In accordance with the hardening, the crosspiece 16 and the picture element assembly 20 are formed. Further, the crosspiece 16 is joined to the optical waveguide plate 14 by the aid of the adhesive 17, and the picture element assembly 20 is joined onto the actuator element 18. Thus, the unit dot 22 (display device 10) is consequently completed.
The precursor of the crosspiece 16 and the precursor of the picture element assembly 20 undergo slight shrinkage during the heat treatment respectively. Of course, the heights of the respective precursors and the heat treatment condition are set so that the crosspiece 16 and the picture element assembly 20 have desired sizes in consideration of the amounts of shrinkage.
However, even when the deposition heights of the respective precursors and the heat treatment condition are set as described above, the size of the picture element assembly 20 is insufficient in some cases. If such a situation occurs, a gap appears between the optical waveguide plate 14 and the upper end surface of the picture element assembly 20, even when it is intended to allow the display device 10 to be in the light emission state. As a result, the luminance of the unit dot 20 is lowered. That is, it is impossible to obtain a desired luminance.